The present invention relates to a technique that can be effectively adapted to a write control system in an electrically erasable and programmable non-volatile memory and more specifically to a technique that can be effectively adapted to a flash memory being capable of simultaneously erasing data, for example, in a predetermined unit.
A flash memory uses, as a memory cell, a non-volatile memory element consisting of a MOSFET of the double-gate structure including a control gate and a floating gate. The write system in the flash memory has been sorted to a system utilizing the FN tunnel phenomenon and a hot-electron system. In the system utilizing the FN tunnel phenomenon, a voltage is applied across the control gate and substrate (or well region) or across the control gate and source or drain and a threshold voltage is changed through implantation or release of charges to and from the floating gate by utilizing the FN tunnel phenomenon.
Meanwhile, in the system utilizing the hot-electron, a threshold voltage is changed through implantation into the floating gate of hot electrons generated in the channel by applying a current across the source and drain under the condition that a high voltage is impressed to the control gate. In the case of the hot-electron system, the charges are generally extracted from the floating gate in the FN tunnel. Moreover, a flash memory is often structured so that data is erased, even when any write system is employed, in unit of memory cell (sector) connected to only one word line or in unit of a plurality of sectors (blocks) using in common the well region and source lines.